Almost all passenger motor vehicles presently produced include some type of impact deployed restraint system to protect vehicle occupants, or others, during a vehicle impact event. Such restraint systems may include, for example, front and side airbags within the passenger compartment, side curtains, inflatable seat belts, and seat belt pretensioners. A restraint system may also include deployable restraints for the protection of pedestrians involved in impacts with the vehicle, such as pedestrian airbags and hood release mechanisms. Sensing systems typically control the deployment of such restraints by detecting the occurrence of a vehicle impact event.
During most impact events, the opportunity to provide occupant restraint exists only for a very brief period of time. Furthermore, inadvertent deployment of a restraint, such as an airbag, is undesirable. Therefore, to be most effective, impact deployed restraints must deploy quickly when needed, and only when actually needed. To this end, impact sensors must be able to discriminate between severe and relatively harmless impact events and also be insensitive to mechanical inputs which are not associated with crash events. Most importantly, however, the design of the sensor must allow for rapid detection of the impact event and transmission of relevant information to allow for effective deployment decisions. The need for a sensor which allows for rapid deployment decisions is particularly great with side airbags, where the crush zone is much smaller than that associated with front airbags, and the time available for a deployment decision is likewise shorter.
Several types of sensors have been used for detection of impact events in vehicles. For example, sensors comprised of piezoelectric cables, accelerometers, pressure sensors and crush-zone switches, have been utilized. While these sensors can operate adequately, it is desirable to improve the ability of vehicle impact sensing systems to discriminate between impact events, such as vehicle crashes, that warrant deployment of a passive restraint, and those that do not, such as a minor impact with a shopping cart. Furthermore, it is desirable to improve the ability of the sensor to provide information regarding the impact, such as its location and relative size, thereby increasing the effectiveness of subsequent deployment decisions.
Consequently, there is a need for an impact sensing system that utilizes sensors capable of relaying information about an impact and making deployment decisions based on such information.